如何从 Java 同时启动服务器和传递命令？

Question

I want to start a server and then pass commands to it. I want to start it from my main() and then pass the instructions. The issue is that when I start the server, then my program is waiting that I stop the server to take next instructions. If possible, I would like to avoid to create a new class. My code looks like:

public static void main(String[] args) throws Exception {
    // run server
    Refine.main(args);


    //commands to pass

The Refine class comes from: https://github.com/OpenRefine/OpenRefine/blob/master/server/src/com/google/refine/Refine.java

Answer 1

I presume that Refine is your "server" main class and that calling Refine.main like that is equivalent to

$ java -cp ... Refine arg1 arg2 ...

In other words, your Refine class has a public static void main(String[] args) entrypoint method.

So how can you get this second main method start the server and then do something else while the server is running?

It depends on how Refine.main works.

• If it works by starting the server on another thread and then returning, then this may work:

   public static void main(String[] args) throws Exception { Refine.main(args); // find handle for service // send commands. }

• If not, then you may need to do something like this:

   public static void main(String[] args) throws Exception { // start server in child thread new Thread(() -> Refine.main(args)).start(); // find handle for service // send commands. }

But in either case, there are other problems to solve:

• You need to be able to obtain the handle (or URL, or whatever) for the server so that you can send it commands.

• You need a way to wait until the server is ready before sending it commands.

The solutions to those will depend on how the Refine class is implemented.

---

UPDATE

Ah... so this the com.google.refine.Refine from OpenRefine.

The Refine.main method is synchronous. If you look at the source code you will see that it is running the server on a private child thread and then waiting for that thread to terminate. In other words, it behaves in the second way that I postulated above.

So to answer your question:

Q: Is it possible to do what you are trying to do without writing your own class?

A: No. It is not possible.

Once you accept that you will have to write a new class, then there are two ways to do it:

1. In the way I suggested above.
2. You could actually write your own modifications for the Refine class. Take a look at what it does.